Secondary trailer brake locking unit



FIG. 1 is a front elevational view of the secondary trailer brake locking unit showing my new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof. 

The ornamental design for a secondary trailer brake locking unit, as shown and described. 